1. Field of the Invention
The invention is directed to a method for regulating the furnace output in incineration plants, particularly waste incineration plants, in which the O.sub.2 moist content measured in the flue gas is used as an overriding reference value regulating variable for regulating the combustible material feed and the measured steam mass flow or the furnace temperature measured in the combustion gas, as desired, is used as a subordinate reference value regulating variable for regulating the primary air supply.
2. Background Prior Art
In a known method of this type, the connection of thermal measured values, e.g. furnace temperature and steam mass flow, and material measured values, e.g. O.sub.2 moist content, makes it possible, on the one hand, to keep the furnace output constant, i.e. to keep the steam mass flow constant, and on the other hand to minimize the emission of harmful material, i.e. to reduce the harmful material contained in the flue gas such as carbon monoxide, dust, hydrocarbons and nitric oxide. A fast-response regulation results from the use of the O.sub.2 moist content as overriding regulating variable within such a regulating concept.
A disadvantage in this method is the fact that the O.sub.2 moist content does not provide defined data about the O.sub.2 dry content and, accordingly, about the true air surplus. However, the measurement of the O.sub.2 dry content of the combustion gas is too inert and, under the existing operating conditions, too unreliable.
When the O.sub.2 moist content, as overriding reference value, and the steam mass flow are kept constant, a shifting of the furnace temperature results during fluctuations in the moisture content of the flue gases. However, these fluctuations in the moisture content of the flue gases can not be avoided because of the sharply diverging composition of combustible material in waste incineration plants. This can lead to a worsening of the emission values at the adjusted and desired output.
On the other hand, if the furnace temperature is kept constant as overriding reference value at an O.sub.2 moist content which is kept constant, a change in the steam mass flow results during fluctuations in the moisture content, which can lead to a worsening of the thermal utilization of the entire plant.
Because of the importance of the low emission values for the environment, the material values, i.e. the O.sub.2 moist content, prevail over the thermal values, that is, the steam mass flow and the furnace temperature. Primary Object of the Invention
Primary object of the invention is to optimize both the emission values and the furnace output proceeding from the two variants of the known method mentioned in the beginning.
This object can be met in two ways.
Proceeding from a method in which the O.sub.2 moist content measured in the flue gas is used as an overriding reference value regulating variable for regulating the combustible material feed and the measured steam mass flow is used as a subordinate reference value regulating variable for regulating the primary air supply, the object is met in that the preselected O.sub.2 moist reference value is changed as a function of the furnace temperature measured in the flue gas.
If, on the other hand, one proceeds from a method in which the O.sub.2 moist content measured in the flue gas is used as an overriding reference value regulating variable for regulating the combustible material feed and the furnace temperature measured in the flue gas is used as a subordinate reference value regulating variable for regulating the primary air supply, the object is met in that the preselected O.sub.2 moist reference value is changed as a function of the measured steam mass flow.
In implementing the first variant of the method, two temperature points are determined as limiting values, wherein the O.sub.2 moist reference value is increased when the upper temperature value is exceeded, while the O.sub.2 moist reference value is reduced when falling below the lower temperature limiting value. Thus, in the first case, the "apparent" air surplus is increased, while in the second case the "apparent" air surplus is reduced. However, the O.sub.2 moist reference value is not influenced as long as the furnace temperature is within the selected limiting values.
The second variant is implemented in a similar manner, wherein two steam mass flow limiting values are selected instead of two temperature limiting values, the O.sub.2 moist reference value being increased or reduced, respectively, when these values are exceeded or when falling below these values. Because of the particular importance of the emission values for the environment, priority is also given to the material values, i.e. the O.sub.2 moist reference value, in the method according to the invention.
An even better regulating accuracy is achieved according to a preferred design of the method in that the rate of change of the measured temperature and steam mass flow values is taken into account in the change of the O.sub.2 moist reference value. Thus, in this design the differential of the temperature change and of the steam mass flow change is considered over time, so that a change in the O.sub.2 moist reference value can be carried out already before reaching the limiting values, so that the operation of the incineration plant is effected in an even more uniform manner because the regulation is more sensitive.
The invention is explained in the following with the aid of the diagrams shown by way of example in the drawing.